Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$117.89	4.732%	$123.4686	$123.47	$123.45	$123.50
Purchase #2	$177.56	9.630%	$194.659	$194.66	$194.65	$194.70
Purchase #3	$235.94	9.337%	$257.9697	$257.97	$257.95	$258.00
Purchase #4	$25.89	10.231%	$28.5388	$28.54	$28.55	$28.50
Purchase #5	$77.93	9.872%	$85.6232	$85.62	$85.60	$85.60
Purchase #6	$198.60	5.571%	$209.664	$209.66	$209.65	$209.70
Purchase #7	$89.98	11.832%	$100.6264	$100.63	$100.65	$100.60
7 purchase totals =	$923.79		$1,000.5497	$1,000.55	$1,000.50	$1,000.60